Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Multimodal Tracking of Controlled Staphylococcus aureus Infections in Mice
    Welling, Mick M. ; Korne, Clarize M. De; Spa, Silvia J. ; Willigen, Danny M. Van; Hensbergen, Albertus W. ; Bunschoten, Anton ; Duszenko, Nikolas ; Smits, Wiep Klaas ; Roestenberg, Meta ; Leeuwen, Fijs W.B. Van - \ 2019
    Bmc Infectious Diseases 5 (2019)7. - ISSN 1471-2334 - p. 1160 - 1168.
    bacterial infection - cell-tracking - fluorescence - multimodal - SPECT - ubiquicidin

    There is a need to develop diagnostic and analytical tools that allow noninvasive monitoring of bacterial growth and dissemination in vivo. For such cell-tracking studies to hold translational value to controlled human infections, in which volunteers are experimentally colonized, they should not require genetic modification, and they should allow tracking over a number of replication cycles. To gauge if an antimicrobial peptide tracer, 99m Tc-UBI 29-41 -Cy5, which contains both a fluorescent and a radioactive moiety, could be used for such in vivo bacterial tracking, we performed longitudinal imaging of a thigh-muscle infection with 99m Tc-UBI 29-41 -Cy5-labeled Staphylococcus aureus. Mice were imaged using SPECT and fluorescence-imaging modalities at various intervals during a 28 h period. Biodistribution analyses were performed to quantitate radioactivity in the abscess and other tissues. SPECT and fluorescence imaging in mice showed clear retention of the 99m Tc-UBI 29-41 -Cy5-labeled bacteria following inoculation in the thigh muscle. Despite bacterial replication, the signal intensity in the abscess only modestly decreased within a 28 h period: 52% of the total injected radioactivity per gram of tissue (%ID/g) at 4 h postinfection (pi) versus 44%ID/g at 28 h pi (15% decrease). After inoculation, a portion of the bacteria disseminated from the abscess, and S. aureus cultures were obtained from radioactive urine samples. Bacterial staining with 99m Tc-UBI 29-41 -Cy5 allowed noninvasive bacterial-cell tracking during a 28 h period. Given the versatility of the presented bacterial-tracking method, we believe that this concept could pave the way for precise imaging capabilities during controlled-human-infection studies.

    Data from: X-Ray Diffraction of Iron Containing Samples: the Importance of a Suitable Configuration
    Mos, Y.M. ; Vermeulen, Arnold C. ; Buisman, C.J.N. ; Weijma, J. - \ 2018
    Wageningen University & Research
    fluorescence - iron - radiation type - X-ray diffraction
    RD results belonging to paper ‘X-Ray Diffraction of Iron Containing Samples: the Importance of a Suitable Configuration’
    Studying fast dynamics in biological complexes : from photosynthesis in vivo to single DNA molecules in vitro
    Farooq, Shazia - \ 2017
    Wageningen University. Promotor(en): Herbert van Amerongen, co-promotor(en): Johannes Hohlbein. - Wageningen : Wageningen University - ISBN 9789463431002 - 149
    biology - dna - proteins - interactions - probability analysis - förster resonance energy transfer - fluorescence - spectroscopy - photosynthesis - biologie - dna - eiwitten - interacties - waarschijnlijkheidsanalyse - förster resonantie-energieoverdracht - fluorescentie - spectroscopie - fotosynthese

    During the last decades, fluorescence spectroscopy has emerged as a powerful tool in the fields of biophysics, biotechnology, biochemistry, cellular biology and the medical sciences. These techniques are highly sensitive, and allow us to study the structure and dynamics of (bio)molecular systems (Valeur 2001). A significant advantage of fluorescence techniques is that they can often be non-invasive and measurements can be performed in real time. In this thesis different advanced fluorescence methods will be used to study two important biological processes: (1) DNA dynamics and (2) plant photosynthesis. The first part aims at improving the smFRET technique for the analysis of DNA dynamics and other fast conformational changes. This improvement is made by combining and developing instrumentation and data evaluation tools. The second part is the continuous development of time-resolved fluorescence spectroscopy methods, as well their application in the field of photosynthesis to study ultrafast processes in thylakoid membranes and leaves. The two fluorescence techniques are technically and conceptually very different, but they are both designed for analysis of biomolecular systems. In this thesis, the techniques are applied to study energy transfer and dynamical changes in DNAs, thylakoid membranes and leaves.

    REFERENCE: VALEUR B 2001. Molecular Fluorescence: Principles and Applications. 1 ed: Wiley-VCH.

    Plantmonitoring op basis van fotosynthese sensoren : ontwikkelen en testen van sensoren
    Dieleman, Anja ; Bontsema, Jan ; Jalink, Henk ; Snel, Jan ; Kempkes, Frank ; Voogt, Jan ; Pot, Sander ; Elings, Anne ; Jalink, Vincent ; Meinen, Esther - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1405) - 86
    teelt onder bescherming - glastuinbouw - kastechniek - sensors - fotosynthese - kooldioxide - energie - energiebesparing - verlichting - kunstlicht - kunstmatige verlichting - ventilatie - kunstmatige ventilatie - fluorescentie - tomaten - solanum lycopersicum - protected cultivation - greenhouse horticulture - greenhouse technology - sensors - photosynthesis - carbon dioxide - energy - energy saving - lighting - artificial light - artificial lighting - ventilation - artificial ventilation - fluorescence - tomatoes - solanum lycopersicum
    The basic process for crop growth and production is photosynthesis. Measuring crop photosynthesis is therefore important to monitor the status of the crop and whether the greenhouse climate is set to the needs of the crop. In this project, two monitoring systems for crop photosynthesis were developed and tested. (1) The crop photosynthesis monitor is a soft sensor that can calculate the CO2 uptake of an entire crop. The basis for these calculations are the balance between CO2 supply and CO2 loss via ventilation and crop photosynthesis. By measuring the CO2 concentration and humidity inside and outside the greenhouse, the crop photosynthesis can be calculated. (2) The CropObserver is a fluorescence sensor that measures the light use efficiency of photosynthesis of a large crop area (3 x 3 m2). The crop receives light pulses from a laser in the top of the greenhouse, the sensor measures the fluorescence signal of the crop. Both sensors were tested in a tomato crop in 2014 with promising results. The sensors functioned without problems and delivered patterns of daily photosynthesis which matched the reference measurements reasonably well up to well.
    Production very closely linked to amount of intercepted light : plant can use a lot of light
    Heuvelink, E. ; Dueck, T.A. ; Noort, F.R. van; Kierkels, T. - \ 2015
    In Greenhouses : the international magazine for greenhouse growers 4 (2015)4. - ISSN 2215-0633 - p. 34 - 35.
    horticulture - greenhouse horticulture - greenhouses - tomatoes - pot plants - photosynthesis - lighting - fluorescence - temperature - light intensity - tuinbouw - glastuinbouw - kassen - tomaten - potplanten - fotosynthese - verlichting - fluorescentie - temperatuur - lichtsterkte
    The photosynthetic process can hardly be bettered. But the utilisation of natural or artificial light certainly leaves room for improvement. In recent years our understanding of light has grown considerably and this has major implications on how we deal with light in horticulture.
    Oral coatings: a study on the formation, clearance and perception
    Camacho, S. - \ 2015
    Wageningen University. Promotor(en): Kees de Graaf, co-promotor(en): Markus Stieger; F. van de Velde. - Wageningen : Wageningen University - ISBN 9789462575653 - 223
    afdeklagen - eiwitten - orale toediening - tong - mond - smering - emulsies - in vivo experimenten - sensorische evaluatie - perceptie - dynamica - zoetheid - fluorescentie - coatings - proteins - oral administration - tongue - mouth - lubrication - emulsions - in vivo experimentation - sensory evaluation - perception - dynamics - sweetness - fluorescence

    Oral coatings are residues of food and beverages that coat the oral mucosa after consumption. Several studies have reported on the lubrication properties in mouth, and the after-feel and after-taste impact of oral coatings. Further, oral coatings have been suggested to influence subsequent taste perception. Although it is well known that oral coatings can influence sensory perception, there was little information available on the chemical composition and physical properties of oral coatings. As such, the aim of this thesis was to understand which factors influence the composition of oral coatings and their sensory perception.

    This study started with the development of an appropriate calibration method for an already described methodology to quantify oil oral coatings: in vivo fluorescence. Further, the samples studied were shifted from pure oil (used on previous studies) to a more realistic food beverage: o/w emulsions. Pig´s tongues are known to be a good model of human tongue. As such, Chapter 2 used pig´s tongues on the calibration of the method, to mimic the fluorescence in mouth of oil coatings. On chapter 2, Confocal Scanning Laser Microscopy images showed that stable o/w emulsions (1-20% (w/w)) stabilised by Na-caseinate created individual oil droplets on the surface of the pigs tongue, as such a new descriptor for oil coatings was developed. Oil fraction, i.e. mass of oil per surface area of the tongue, was shown to be higher on the back compared to the front anterior part of the tongue. This is thought to be due to the morphology of the tongue and abrasion of the oil coating owed to the rubbing with the palate. Further, in vivo measurements showed that oil fraction deposited on the tongue increased linearly with oil content of o/w emulsions. Coating clearance from the tongue was a fast process with around 60% of the oil being removed on the first 45s. After-feel perception (Fatty Film and Flavour Intensity) was shown to be semi-logarithmic related to oil fraction on the tongue.

    Chapter 3, further investigated different properties of 10% (w/w) o/w emulsions that influence the oil fraction deposited on the tongue, its clearance and after-feel perception. Three different properties were studied: protein type, protein content and viscosity of the o/w emulsions. To study the influence of protein type, two different proteins which behave differently in-mouth were studied: Na-caseinate - creates emulsions which do not flocculate under in mouth conditions, and lysozyme – creates emulsions which flocculate under in mouth conditions. To study the influence of protein content, three concentrations of Na-caseinate and lysozyme were used (0.2, 3, 5.8% (w/w) all in excess to stabilize the water/oil interface). To study the influence of viscosity of o/w emulsions, three o/w emulsions stabilized with 3% (w/w) Na-caseinate were thickened with varying concentrations of xanthan gum (0-0.5%) (w/w).

    Generally, the irreversible flocculation of lysozyme stabilized emulsions with saliva did not create a significant difference on oil deposition compared to emulsions stabilized with Na-caseinate, immediately after expectoration of the emulsions. Nevertheless, lysozyme stabilised emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction on the tongue for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions. The presence of thickener decreased deposition of oil on tongue, although viscosity differences (i.e., thickener content) did not affect oil fraction. After-feel perception of creaminess and fatty-film was strongly influenced by the presence of thickener likely due to lubrication in-mouth, i.e., the higher the concentration of thickener in the emulsions the stronger was the perception. Oral coatings perception was further influenced by the protein used in the emulsions, with Na-caseinate stabilised emulsions creating coatings with higher perception on creaminess and fatty-film.

    Chapter 2 and chapter 3 provided knowledge on the deposition and clearance of oil coatings, but little was known on the formation of oil coatings. Chapter 4 focused on the formation of oil coatings formed by Na-caseinate stabilised o/w emulsions (1-20% (w/w)). The formation of oil coatings was a rapid process, where the maximum oil deposition was achieved at normal drinking behaviour (~3s). Further, in Chapter 4 we investigated the hypothesis often referred on literature, in which oil coatings form a physical barrier which prevents tastants to reach the taste buds, and thus create a reduction on taste perception. It was concluded that oil coatings formed by emulsions within one sip did not affect subsequent sweetness perception of sucrose solutions. We suggested that the oil droplets deposited on the tongue (as seen on chapter 2) did not form a hydrophobic barrier that is sufficient to reduce the accessibility of sucrose to the taste buds and consequently does not suppress taste perception.

    Previous chapters focused on oral coatings formed by liquid o/w emulsions, however studies describing oral coatings formed by semi-solids and solids are scarce. As such, chapter 5 focused on the formation, clearance and sensory perception of fat coatings from emulsion-filled gels. Four emulsion-filled gelatin gels varying in fat content and type of emulsifier (whey protein isolate - created fat droplets bound to matrix; tween 20 - created fat droplets unbound to matrix) were studied. As in for oil coatings formed by liquid o/w emulsions, fat coatings formed by emulsion-filled gels reach their maximum deposition in the first seconds of mastication. This suggests that the first bites are the most relevant for the formation of fat coatings on the tongue. Further, fat fraction deposited on tongue increased when oral processing time of the gels increased. This trend was clearer for gels with higher fat content (15%) compared to gels with lower fat content (5%). Fatty perception increased with increasing mastication time, and decreased after expectoration with increasing clearance time. Fat fraction deposited on tongue and fatty perception are higher in gels with unbound droplets compared to bound droplets, as well as in gels with 15% fat compared to 5% fat.

    To elucidate the role of protein on oral coatings, Chapter 6 focused on the development of a method to quantify protein in the oral coatings. Further, Chapter 6 studied the influence of protein content, in-mouth protein behaviour (lysozyme - protein which creates flocs with saliva vs. Na-Caseinate - protein which does not create flocs with saliva) and presence of thickener on the formation of protein oral coatings and sensory perception of protein coatings. Protein coatings were collected from the front and middle part of the anterior tongue using cotton swabs after subjects orally processed protein solutions for different time periods. Protein concentration of the coating (mass protein/mass coating) was quantified with the Lowry method. Similarly to oil/fat coatings, results show protein coatings are formed rapidly, reaching maximum deposition on the first seconds of the samples´ oral processing. Further, different protein in mouth-behaviour (Na-caseinate vs. lysozyme) did not create differences on protein deposition on the tongue. Presence of xanthan-gum in the processed samples decreased protein deposition on the tongue, compared to when samples without xanthan-gum were processed. The perception of protein coatings was strongly influenced by the viscosity and protein used in the samples. Higher viscosity of the samples lead to higher intensity on creaminess and thickness. Lysozyme samples created coatings with high sweetness and astringent intensity, which is related to the molecular structure of the protein.

    Changes in the viscosity of beverages can cause changes in thickness perception. The changes in thickness perception can be accompanied by differences in other sensory properties, such as sweetness and creaminess which might be undesirable when reformulating beverages or developing new products. Knowledge on the differences by which viscosity of beverages can be modified to create a difference in sensory perception is currently lacking. Chapter 7 focus on the determination of the Just Noticeable Difference (the minimal difference that can be detected between two stimuli) for thickness perception of beverages. Oral thickness sensitivity (K=0.26) was found to be comparable to literature values for kinesthetic food firmness and spreadability, creaminess, sourness and bitterness perception.

    The aim of this thesis was to determine and characterize factors influencing oral coatings and their sensory perception. For this purpose, reliable methods to quantify oil and protein deposited on the tongue had to be developed to later study the macronutrients deposition. Further, the influence of stimulus properties on the formation and clearance dynamics of oral coatings and their impact on sensory perception were investigated.

    Probing functional (re)organisation in photosynthesis by time-resolved fluorescence spectroscopy
    Ünlü, C. - \ 2015
    Wageningen University. Promotor(en): Herbert van Amerongen. - Wageningen : Wageningen University - ISBN 9789462572829 - 118
    algen - fotosynthese - light harvesting complexen - fotosysteem ii - fluorescentie - spectroscopie - chlamydomonas reinhardtii - algae - photosynthesis - light harvesting complexes - photosystem ii - fluorescence - spectroscopy - chlamydomonas reinhardtii

    Summary

    The possible mechanisms for reorganisation of outer LHCs of PSII (LHCII) upon state transitions in Chlamydomonas reinhardtii have been discussed for several decades [38, 43-54]. For a long time people adhered to the opinion that upon the transition from state 1 to state 2, 80% of LHCII detaches from PSII and attaches completely to PSI in Chlamydomonas reinhardtii [38, 45]. This thesis provides new insights for the mechanism of state transitions in Chlamydomonas reinhardtii. In the remainder of this thesis, the role of minor light-harvesting complexes in excitation energy transfer to reaction centers of photosystem II are discussed as well as multiexciton dynamics of the alloyed ZnCdTe quantum dots are studied in detail.

    In chapter 2, we demonstrate with picosecond-fluorescence spectroscopy on C. reinhardtii cells that although LHCs indeed detach from Photosystem II in state-2 conditions only a fraction attaches to Photosystem I. The detached antenna complexes become protected against photodamage via shortening of the excited-state lifetime. It is discussed how the transition from state 1 to state 2 can protect C. reinhardtii in high-light conditions and how this differs from the situation in plants.

    In chapter 3, we study the picosecond fluorescence properties of Chlamydomonas reinhardtti over a broad range of wavelengths at 77K. It is observed that upon going from state 1 (relatively high 680nm/720nm fluorescence ratio) to state 2 (low ratio), a large part of the fluorescence of LHC/PSII becomes substantially quenched, probably because of LHC detachment from PSII, whereas the fluorescence of PSI hardly changes. These results are in agreement with the proposal in chapter 2 that the amount of LHC moving from PSII to PSI upon going from state 1 to state 2 is very limited.

    In chapter 4, we used picosecond-fluorescence spectroscopy to study excitation-energy transfer (EET) in thylakoids membranes isolated from A. thaliana wild-type plants and knockout lines depleted of either two (koCP26/24 and koCP29/24) or all minor Lhcs (NoM). In the absence of all minor Lhcs, the functional connection of LHCII to the PSII cores appears to be seriously impaired whereas the “disconnected” LHCII is substantially quenched. For both double knock-out mutants, excitation trapping in PSII is faster than in NoM thylakoids but slower than in WT thylakoids. In NoM thylakoids, the loss of all minor Lhcs is accompanied by an over-accumulation of LHCII, suggesting a compensating response to the reduced trapping efficiency in limiting light, which leads to a photosynthetic phenotype resembling that of low-light-acclimated plants. Finally, fluorescence kinetics and biochemical results show that the missing minor complexes are not replaced by other Lhcs, implying that they are unique among the antenna subunits and crucial for the functioning and macro-organization of PSII.

    In chapter 5, we have performed picosecond fluorescence measurements on ZnCdTe ternary quantum dots at room temperature by using a streak-camera setup in order to investigate in detail the fluorescence kinetics for ZnCdTe quantum dots with different size and structure by using different excitation laser intensities. Our data show that the changes in fluorescence kinetics are mostly related to the changes in structure and size. In heterogeneous structured ZnCdTe quantum dots, the fluorescence kinetics become faster as compared to homogeneous structured ZnCdTe quantum dots. Also, in both homogeneous and heterogeneous ZnCdTe quantum dots, a new peak is observed in the high-energy region of the emission spectrum when using high excitation intensities, which shows that the radiative processes that occur from higher energy states become more favoured as the excitation intensity increases.

    CF camera on platform (side crop viewer)
    Gorbe Sanchez, E. - \ 2015
    tuinbouw - glastuinbouw - kasproeven - tomaten - botrytis - stengels - fluorescentie - fotosynthese - opnameapparatuur - conferenties - horticulture - greenhouse horticulture - greenhouse experiments - tomatoes - botrytis - stems - fluorescence - photosynthesis - recording instruments - conferences
    Experiment on how early the CF camera can detect botrytis infection in tomato stems inoculated with botrytis spores. Poster van PlantgezondheidEvent 12 maart 2015.
    Partitioning of humic acids between aqueous solution and hydrogel. 3. Microelectrodic dynamic speciation analysis of free and bound humic metal complexes in the gel phase
    Yasadi, K. ; Pinheiro, J.P. ; Zielinska, K. ; Town, R.M. ; Leeuwen, H.P. van - \ 2015
    Langmuir 31 (2015)5. - ISSN 0743-7463 - p. 1737 - 1745.
    dissolved organic-matter - stability-constants - alginate gel - thin-films - adsorption - ions - fluorescence - substances - cells - soil
    The hydrogel/water partitioning of the various species in the cadmium(II)/soil humic acid (HA) system is studied for two types of gel, using in situ microelectrodic voltammetry. Under the conditions of this work, with HA particles of ca. 25 and 125 nm radius, the CdHA complex is shown to be close to nonlabile toward a 12.5 µm radius microelectrode. This implies that its kinetic contribution to Cd2+ reduction at the medium/microelectrode interface is practically negligible. The polyacrylamide (PAAm) gels equilibrate with the aqueous medium under significant sorption of HA at the gel backbone/gel medium interface, which in turn leads to induced sorption of Cd(II) in the form of immobilized gel-bound CdHA. The rather high total Cd content of the PAAm gel suggests that the binding of Cd2+ by the hydrophobically gel-bound HA is stronger than that for dispersed HA particles. Still, the intraparticulate speciation of Cd(II) over Cd2+ and CdHA corresponds to an intrinsic stability constant similar to that for simple monocarboxylate ligands such as acetate. Alginate gels are negatively charged, and their free [Cdaq2+] is higher than that in the medium by the corresponding Donnan coefficient. On top of that, Cd2+ is specifically sorbed by the gel backbone/gel medium interface to reach accumulation factors as high as a few tens. HA and CdHA accumulate in the outer 20 µm film of gel at the gel/water interface of both gels, but they do not penetrate into the bulk of the alginate gel. Overall, the gel/water interface dictates drastic changes in the speciation of Cd/HA as compared to the aqueous medium, with distinct features for each individual type of gel. The results have broad significance, for example, for predictions of reactivity and bioavailability of metal species which inherently involve partitioning and diffusion into diverse gel layers such as biointerfacial cell walls, biofilm matrices, and mucous membranes.
    Partitioning of humic acids between aqueous solution and hydrogel. 2. Impact of physicochemical conditions
    Zielinska, K. ; Town, R.M. ; Yasadi, K. ; Leeuwen, H.P. van - \ 2015
    Langmuir 31 (2015)1. - ISSN 0743-7463 - p. 283 - 291.
    ionic-strength - alginate gel - heavy-metals - fluorescence - substances - ph - aggregation - media - soil - spectroscopy
    The effects of the physicochemical features of aqueous medium on the mode of partitioning of humic acids (HAs) into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) were explored. Experiments were performed under conditions of different pH and ionic strength as well as in the presence or absence of complexing divalent metal ions. The amount of HA penetrating the gel phase was determined by measuring its natural fluorescence by confocal laser scanning microscopy. In both gel types, the accumulation of HA was spatially heterogeneous, with a much higher concentration located within a thin film at the gel surface. The thickness of the surface film (ca. 15 µm) was similar for both types of gel and practically independent of pH, ionic strength, and the presence of complexing divalent metal ions. The extent of HA accumulation was found to be dependent on the composition of the medium and on the type of gel. Significantly more HA was accumulated in PAAm gel as compared to that in alginate gel. In general, more HA was accumulated at lower background salt concentration levels. The distribution of different types of HA species in the gel body was linked to their behavior in the medium and the differences in physicochemical conditions inside the two phases.
    LUMINEX®: fast fluorescent detection : multiplex detection for the agricultural and food industries
    Bergervoet, J.H.W. ; Currie, H.T. - \ 2014
    precisielandbouw - teeltsystemen - gewasbescherming - voedselgewassen - detectie - enzymimmunoassay - elisa - immunoassay - voedselveiligheid - fluorescentie - precision agriculture - cropping systems - plant protection - food crops - detection - enzyme immunoassay - elisa - immunoassay - food safety - fluorescence
    Luminex®: Detection of mycotoxins, pathogenic fungi, proteins, DNA/RNA
    Light harvesting in a fluctuating antenna
    Chmeliov, J. ; Trinkunas, G. ; Amerongen, H. van; Valkunas, L. - \ 2014
    Journal of the American Chemical Society 136 (2014)25. - ISSN 0002-7863 - p. 8963 - 8972.
    excitation-energy transfer - photosystem-ii supercomplexes - thylakoid membrane - charge separation - crystal-structure - photosynthetic systems - photoprotective mode - lhcii complex - fluorescence - annihilation
    One of the major players in oxygenic photosynthesis, photosystem II (PSII), exhibits complex multiexponential fluorescence decay kinetics that for decades has been ascribed to reversible charge separation taking place in the reaction center (RC). However, in this description the protein dynamics is not taken into consideration. The intrinsic dynamic disorder of the light-harvesting proteins along with their fluctuating dislocations within the antenna inevitably result in varying connectivity between pigment–protein complexes and therefore can also lead to nonexponential excitation decay kinetics. On the basis of this presumption, we propose a simple conceptual model describing excitation diffusion in a continuous medium and accounting for possible variations of the excitation transfer rates. Recently observed fluorescence kinetics of PSII of different sizes are perfectly reproduced with only two adjustable parameters instead of the many decay times and amplitudes required in standard analysis procedures; no charge recombination in the RC is required. The model is also able to provide valuable information about the structural and functional organization of the photosynthetic antenna and in a straightforward way solves various contradictions currently existing in the literature.
    Interaction of flavan-3-ol derivatives and different caseins is determined by more than proline content and number of proline repeats
    Bohin, M.C. ; Vincken, J.P. ; Westphal, A.H. ; Tripp, A.M. ; Dekker, Peter ; Hijden, H.T.W.M. ; Gruppen, H. - \ 2014
    Food Chemistry 158 (2014). - ISSN 0308-8146 - p. 408 - 416.
    food proteins - binding - astringency - polymerization - precipitation - complexation - fluorescence - procyanidins - polyphenols - gallate
    Interactions of Type A and B flavan-3-ol dimers (procyanidins) and several monomeric flavan-3-ols, with a-casein and ß-casein, were investigated. Binding affinities measured were related to the ligands structure, including several properties (e.g. intrinsic flexibility (number of rotatable bonds) and hydrophobicity), and to the amino-acid composition of the caseins. A monomeric flavan-3-ol esterified with gallic acid (EGCG) had a five to ten times higher affinity to caseins compared to the non-galloylated dimeric flavan-3-ols. In this case, the larger number of rotatable bonds in EGCG might be accountable for this difference. Comparing flavan-3-ol dimers, intrinsic flexibility did not consistently promote interactions, as procyanidin A1 displayed a higher affinity to a-casein than the supposedly more flexible B-type dimers investigated. Despite its higher content of proline, compared to a-casein, ß-casein did not always have a higher affinity for the ligands investigated (e.g. no interaction with procyanidin A1 detected). These results suggest that more factors than proline content and the number of proline repeats govern phenolic–casein interactions.
    Balancing the organic load and light supply in symbiotic microalgal–bacterial biofilm reactors treating synthetic municipal wastewater
    Boelee, N.C. ; Temmink, B.G. ; Janssen, M. ; Buisman, C.J.N. ; Wijffels, R.H. - \ 2014
    Ecological Engineering 64 (2014). - ISSN 0925-8574 - p. 213 - 221.
    afvalwaterbehandeling - biofilms - symbiose - algen - bacteriën - heterotrofe micro-organismen - fotosynthese - acetaten - stikstof - fosfor - nitrificatie - denitrificatie - biologische waterzuiveringsinstallaties - biobased economy - waste water treatment - biofilms - symbiosis - algae - bacteria - heterotrophic microorganisms - photosynthesis - acetates - nitrogen - phosphorus - nitrification - denitrification - biological water treatment plants - biobased economy - activated-sludge - nutrient removal - growth - phytoplankton - fluorescence - enhancement
    Symbiotic microalgal–bacterial biofilms can be very attractive for municipal wastewater treatment. Microalgae remove nitrogen and phosphorus and simultaneously produce the oxygen that is required for the aerobic, heterotrophic degradation of organic pollutants. For the application of these biofilms in new wastewater treatment systems, the engineering aspects need to be investigated to obtain a balanced system where no additional oxygen is required. In this study symbiotic microalgal–bacterial biofilms were grown in flow cells with ammonium and phosphate, and with acetate as biodegradable organic pollutant at a hydraulic retention time of 4.5 h. The symbiotic biofilms removed acetate from 323 mg/L to 39 mg/L without an external oxygen or carbon dioxide supply at a removal rate of 43 g COD/m2/d. Ammonium and phosphate could not be completely removed, but removal rates of 3.2 g/m2/d and 0.41 g/m2/d were obtained, respectively. Further nitrogen removal may be obtained by nitrification and denitrification as the biofilm obtained a considerable heterotrophic denitrification capacity. The symbiotic relationship between microalgae and aerobic heterotrophs was proven by subsequently removing light and acetate. In both cases this resulted in the cessation of the symbiosis and in increasing effluent concentrations of both acetate and the nutrients ammonium and phosphate. Future research should investigate the dimensioning of an up-scaled symbiotic biofilm reactor, and the possibilities to obtain additional nitrogen and phosphorus removal under day–night cycles utilizing real wastewater.
    Verification of fresh grass feeding, pasture grazing and organic farming by FTIR spectroscopy analysis of bovine milk
    Capuano, E. ; Rademaker, J. ; Bijgaart, H. van den; Ruth, S.M. van - \ 2014
    Food Research International 60 (2014). - ISSN 0963-9969 - p. 59 - 65.
    near-infrared spectroscopy - fatty-acid-composition - total mixed ration - geographic origin - edible oils - dairy-cows - fluorescence - cheese - food - differentiation
    In the present study, a total of 116 tank milk samples were collected from 30 farms located in The Netherlands and analysed by Fourier-transform infrared (FTIR) spectroscopy. Samples were collected in April, May and June 2011 and in February 2012. The samples differed in the time spent by the cows on pasture, presence/absence of fresh grass in the daily ration and the farming system (organic/biodynamic or conventional). Classification models based on partial least square discriminant analysis (PLS-DA) of FTIR spectra were developed for the prediction of fresh grass feeding, pasture grazing and organic farming. The PLS-DA model discriminated between milk from cows that had fresh grass in the daily ration and milk from cows that had not fresh grass with sensitivity and specificity values of 88% and 83% in external validation and all the samples from cows that had no fresh grass collected in spring were correctly classified. The PLS-DA model developed for the authentication of pasture grazing showed comparable accuracy when the whole sample set is considered but was less accurate on the spring samples (75% of samples from cows indoors in spring correctly classified). Discrimination of organic and conventional milk was also accomplished with acceptable accuracy with % correct classification of 80% and 94% respectively in external validation. The results suggest that milk FTIR spectra contain valuable information on cows' diet that can be used for authentication purposes.
    Antibioticagebruik achterhaald via bot
    Rijke, E. de; Raamsdonk, L.W.D. van; Nielen, M.W.F. - \ 2013
    Voedingsmiddelentechnologie 23 (2013). - ISSN 0042-7934 - p. 30 - 31.
    antibiotica - pluimveehouderij - vleeskuikens - fluorescentie - tests - voedselveiligheid - pluimveevlees - antibiotics - poultry farming - broilers - fluorescence - food safety - poultry meat
    Om het ontstaan van antibioticaresistente bacteriën tegen te gaan, mogen pluimveehouders antibiotica alleen nog therapeutisch gebruiken. RIKILT ontwikkelde een fluorescentietest waarmee relatief eenvoudig en snel kan worden achterhaald of kuikens antibiotica hebben gekregen en ook of de antibiotica tegen ziekte of meer als groeibevorderaar zijn ingezet.
    Analysis of steady-state Förster resonance energy transfer data by avoiding pitfalls: Interaction of JAK2 tyrosine kinase with N-methylanthraniloyl nucleotides.
    Niranjan, Y. ; Ungureanu, D. ; Hammarén, H. ; Sanz-Sanz, A. ; Westphal, A.H. ; Borst, J.W. ; Silvennoinen, O. ; Hilhorst, M.H. - \ 2013
    Analytical Biochemistry 442 (2013)2. - ISSN 0003-2697 - p. 213 - 222.
    pseudokinase domain - protein-kinase - fluorescence - atp - binding - receptor - analogs - site - autophosphorylation - mechanism
    Förster resonance energy transfer (FRET) between the fluorescent ATP analogue 2'/3'-(N-methyl-anthraniloyl)-adenosine-5'-triphosphate (MANT–ATP) and enzymes is widely used to determine affinities for ATP–protein binding. However, in analysis of FRET fluorescence data, several important parameters are often ignored, resulting in poor accuracy of the calculated dissociation constant (Kd). In this study, we systematically analyze factors that interfere with Kd determination and describe methods for correction of primary and secondary inner filter effects that extend the use of the FRET method to higher MANT nucleotide concentrations. The interactions of the fluorescent nucleotide analogues MANT–ATP, MANT–ADP [2'/3'-O-(N-methylanthraniloyl) adenosine diphosphate], and MANT–AMP [2'/3'-O-(N-methylanthraniloyl) adenosine monophosphate] with the JAK2 tyrosine kinase domain are characterized. Taking all interfering factors into consideration, we found that JAK2 binds MANT–ATP tightly with a Kd of 15 to 25 nM and excluded the presence of a second binding site. The affinity for MANT–ADP is also tight with a Kd of 50 to 80 nM, whereas MANT–AMP does not bind. Titrations of JAK2 JH1 with nonhydrolyzable ATP analogue MANT–ATP-¿-S [2'/3'-O-(N-methylanthraniloyl) adenosine-5'-(thio)- triphosphate] yielded a Kd of 30 to 50 nM. The methods demonstrated here are applicable to other enzyme–fluorophore combinations and are expected to help improve the analysis of steady-state FRET data in MANT nucleotide binding studies and to obtain more accurate results for the affinities of nucleotide binding proteins.
    Kasklimaatregeling op basis van fotosynthese-metingen: wat zijn de mogelijkheden? : verslag van het eerste werkpakket van het project " Energie besparen door sturing van licht en CO2 op basis van gewasbehoefte"
    Dieleman, J.A. ; Pot, S. ; Snel, J.F.H. ; Kromdijk, J. ; Jalink, H. ; Bontsema, J. - \ 2013
    Wageningen : Wageningen UR Glastuinbouw (Rapporten GTB 1270) - 26
    glastuinbouw - klimaatregeling - fotosynthese - gasuitwisseling - fluorescentie - meting - gewasmonitoring - behoeftenbepaling - lichtregiem - kooldioxide - greenhouse horticulture - air conditioning - photosynthesis - gas exchange - fluorescence - measurement - crop monitoring - needs assessment - light regime - carbon dioxide
    Het klimaat in een kas wordt ingesteld om een optimale gewasfotosynthese, assimilatenverdeling en plantvorm te realiseren. Om momentaan het kasklimaat aan te kunnen passen aan de behoeftes van de plant is het van groot belang inzicht te hebben in de directe gevolgen van aanpassingen in het klimaat op de plant prestaties, in het bijzonder op de fotosynthese. Dit is te doen met de volgende methodes: 1. Gasuitwisseling van bladeren: nauwkeurige metingen van de fotosynthese van een stukje blad, met draagbare meetapparatuur. 2. Plantivity: een commercieel verkrijgbare meter die de fluorescentie van een stukje blad meet. 3. Kas-in-kas: een niet-geklimatiseerde meetkamer waarin CO 2 opname van een aantal planten gemeten kan worden. 4. Fluorescentie-imaging: fluorescentie metingen op afstand aan een groter oppervlakte gewas. 5. Fotosynthese-monitor: soft-sensor waarmee de CO 2 opname van een kas berekend wordt op basis van ventilatievoud en metingen van de CO 2 concentratie binnen en buiten de kas. Uit twee workshops met telers bleek dat zij fotosynthese als een belangrijk proces beschouwen in de teelt van hun gewas, en dat zij de fotosynthese van hun gewas graag momentaan online zouden willen meten. Het is daarom wenselijk door te gaan met de ontwikkeling van een robuust en betrouwbaar meetsysteem voor de gewasfotosynthese
    Effect of Maillard reaction on biochemical properties of peanut 7S globulin (Ara h 1) and its interaction with a human colon cancer cell line (Caco-2)
    Teodorowicz, M. ; Fiedorowicz, E. ; Kostyra, H. ; Wichers, H.J. ; Kostyra, E. - \ 2013
    European Journal of Nutrition 52 (2013)8. - ISSN 1436-6207 - p. 1927 - 1938.
    reaction-products - in-vitro - colorimetric assay - model system - fluorescence - proliferation - allergens - digestion - antioxidant - prevalence
    Purpose The purpose of this study was to determine the influence of Maillard reaction (MR, glycation) on biochemical and biological properties of the major peanut allergen Ara h 1. Methods Three different time/temperature conditions of treatment were applied (37, 60, and 145 °C). The extent of MR was assessed by SDS-PAGE, loss of free amino groups, fluorescence intensity, content of bound sugar and fructosamine. The Caco-2 model system was applied to study effects of hydrolysed and non-hydrolysed Ara h 1 on proliferation and interleukin-8 (IL-8) secretion from Caco-2 cells. Results We demonstrated significant differences in the biochemical properties of Ara h 1 glycated at different time/temperature conditions. Glycation of Ara h 1 at 37 °C was shown to cause least biochemical changes, not limiting pepsin hydrolysis. Loss of free amino groups, increase of fluorescence and brown colour of Ara h 1 glycated at 60 and 145 °C indicated advanced and final stages of MR. Non-treated Ara h 1 inhibited Caco-2 cell proliferation and stimulated IL-8 secretion. This effect was less pronounced for glycated Ara h 1. Incubation of Caco-2 cells with non-hydrolysed Ara h 1, glycated at the temperature of 37 and 60 °C, did not stimulate IL-8 secretion. Conclusion Each applied time/temperature-treatment combination caused different biochemical changes of Ara h 1, underlining diversity of formed MRPs. MR, independently of temperature/time conditions, reduced the pro-inflammatory properties of native Ara h 1, reflected in stimulation of IL-8 secretion from intestinal epithelial cells.
    Light harvesting and photoprotection in Cyanobacteria
    Tian, L. - \ 2013
    Wageningen University. Promotor(en): Herbert van Amerongen. - [S.l.] : s.n. - ISBN 9789461735294 - 167
    cyanobacteriën - fotosynthese - light harvesting complexen - fluorescentie - lichtverdeling - cyanobacteria - photosynthesis - light harvesting complexes - fluorescence - light distribution

    The process of photosynthesis has been studied for centuries, but despite a large amount of progress, there are still many aspects that are not fully understood. An important part of the progress is the fact that many structures of photosynthetic complexes have been resolved 1,2and these complexes have been studied separately in great detail, amongst other with ultrafast spectroscopic techniques. These studies allow to monitor excitation-energy transfer (EET) and charge separation (CS), the first crucial processes after the absorption of a photon. Many picosecond studies have also been performed in vivo in the past before the crystal structures were known, but due to an additional lack of knowledge about the organization and composition of the thylakoid membrane where most of the EET and CS processes take place, the obtained results were difficult to interpret. More recently, new interest has arisen in in vivo studies on photosynthetic organisms because a lot of molecular and organizational information has been obtained but also because the spectroscopic techniques have improved and mutants have become available that allow to study the effect of specific modifications in the organisms. This thesis focuses on the study of the light energy harvesting processes of photosynthetic complexes in cyanobacteria in general by using time-resolved fluorescence techniques, and with particular emphasis on the study of the in vivo protective process of non-photochemical quenching (NPQ) that is induced in the presence of high intensities of blue-green light.

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